The positive pressure (1/2" WG) gas flow on a window housing
and embedment liner caused by a dry inert gas purge will maintain a dry
window in a "like new" condition for virtually its entire
design lifetime. The purge gas precludes the entrance of
contaminates such as moisture, dust and oxygen into the window
housing and embedment liner cavities. Since all windows
"breathe" due to the changes in atmosphere pressure and
temperature, the positive pressure purge system maintains a non-contaminating
inert atmosphere at the internal glass surfaces under any atmospheric
change condition, preserving the integrity of the window design.
Purge capabilities are provided by an inert gas manifold as a facility
system, which supplies the inert gas to the window housing and
embedment liner/window housing cavity through a shutoff valve and
rotometer on each line. A low pressure orifice for the window
housing and liner allow a very minor inert gas flow rate to occur at
all times. The flow orifices are designed for a flow rate of
approximately .25 - 2.0 ft3/24 hr period at a pressure differential of
1/2" WG, depending on the size of the window assembly.
Attempting to "lock-in" the inert gas and eliminating
the gas purge will result in gradual window viewing system
deterioration over the following next several years, generally by
the condensation of water vapor and dust filming on the interior glass
surfaces. The
surfaces will gradually deteriorate under the same chemical
mechanisms described under the heading Shielding Window Oil.
Restoring the gas purge will not restore the damage already
inflicted on the glass surfaces. "Locking in" the inert
gas also has the potential of breaking the cold side cover plate due
to atmospheric pressure changes and operational thermal gradients.
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Data and information contained in the tutorial was written by Dale A. Tobias, Premier Technology, Inc. and Hienz E. Hoffman and William G. Wash, Schott Glass Technologies, Inc. and may be reproduced only with written consent.
For information, contact Lyle Freeman
Vice President of Business Development
(208) 782-9129 lfreeman@ptius.net
